The invention lies in the field of light-emitting transmission devices, particularly for optical data transmission purposes, which are equipped with a so-called monitoring unit for power control. Specifically, for many applications, it is desirable or essential, for example for safety reasons, to stabilize the output power of a transmitter, which is usually a laser, irrespective of temperature fluctuations and aging effects, for example. In the case of edge or side-radiating lasers, a power monitor can be arranged on that laser side or laser edge which is not intended for useful power output. The radiation (loss) emanating at that side can thus be used for control purposes.
Relatively recent developments and progress in production processes increasingly also allow economic production of so-called vertically emitting laser transmitters (VCSEL=Vertical Cavity Surface Emitting Laser). For the purpose of satisfying high quality demands towards a constant output power, however, the VCSEL transmitters require a control unit with a monitoring device.
In that regard, the invention relates to an optical transmission device having an optical transmitter with an emission zone. Upon activation, the transmitter emits radiation vertically with respect to a covering surface of the transmitter. The device further has a reflection surface which reflects a portion of the emitted radiation toward the transmitter side, and a monitor receiver is arranged on the transmitter side with an optically sensitive reception zone on which at least a portion of the reflected radiation impinges.
Published international application WO 95/18479 (see introduction) describes a basic design in which a fraction of the radiation emitted from a vertically radiating transmitter reaches a monitor unit (photodiode) via a beam splitter. The output signal from the monitor unit is input into a control circuit which controls the drive current of the laser (operating point) such that a desired transmission output power is achieved. On that basis, WO 95/18479 describes an optical transmission device in which a vertically emitting laser (VCSEL) has an integrated photodetector which evaluates radiation emanating on the underside of the laser. That prior art design is comparatively complex and presupposes that the laser transmitter and monitor unit are integrally formed. It is thereby not possible to fit the transmitter with a monitoring unit at a later time or as an option.
A transmission device of the type mentioned above is disclosed in published European application EP 0 786 838 A2 (FIG. 4E). To produce an integrated controlled laser light source, that transmission device is provided with a vertically radiating laser as transmitter, which has an emission zone radiating perpendicularly to a covering surface. A monitor unit having an optically sensitive reception zone is provided for power control. The emitted radiation arrives at a spherical lens whose surface on the transmitter side acts as a reflection surface. The reflection surface reflects a portion of the emitted radiation back onto the reception zone, which can be arranged around or next to the emission zone. The predominant portion of the emitted radiation passes through the spherical lens to a coupling zone. The coupling zone may be formed, for example, as an optical conductor connector receptacle.
The generally slightly divergent course of the emitted radiation means that it broadens out, so that, with regard to the resultant reduced intensity, either a reception zone with a comparatively large area must be provided or else a lower yield must be accepted.
It is accordingly an object of the invention to provide a transmission device, which overcomes the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and which renders it possible that as large a proportion of the reflected radiation as possible is able to impinge on as small a reception zone as possible.
With the foregoing and other objects in view there is provided, in accordance with the invention, an optical transmission device, comprising:
an optical transmitter disposed at a transmitter side, the transmitter having a covering surface and an emission zone for emitting radiation vertically with respect to the covering surface;
a reflection surface spaced apart from the covering surface for reflecting a portion of the radiation back toward the transmitter side;
a monitor receiver disposed at the transmitter side, the receiver being formed with an optically sensitive reception zone; and
an intermediate body disposed between the reflection surface and the reception zone, the intermediate body being formed with a reflecting circumferential surface;
wherein the reception zone of the receiver receives radiation reflected from the reflection surface, and whereby at least a part of the portion of the radiation reflected from the reflection surface passes from the circumferential surface to the reception zone.
In other words, the objects are satisfied with the intermediate body that is formed with a reflecting circumferential surface and is arranged between the reflection surface and the reception zone. At least some of the reflected radiation is thereby forwarded to the reception zone via the circumferential surface.
A significant advantage of the invention is that a considerable increase in the radiation yield which can be used for control purposes is made possible with just a single, simple and inexpensive additional part. This means that, in comparison with conventional arrangements, a relatively small and thus inexpensive reception zone can be provided, so that, overall, the production costs for the transmission device according to the invention can be significantly reduced. A further advantage is that light travelling from the reflecting circumferential surface to the reception zone does not stray and hence crosstalk effects can be effectively avoided, particularly in the case of multichannel transmission devices.
In accordance with an added feature of the invention, the intermediate body is a solid body and the reflecting circumferential surface is formed by a curved surface of the solid body. This refinement of the invention is particularly preferred in terms of production technology. The light reflected back from the reflection surface and input into the intermediate body passes through the intermediate body and, if appropriate, is reflected by the outer curved surface of the intermediate body. The curved surface, of course, is made reflective for this purpose.
In accordance with an additional feature of the invention, the intermediate body is formed with an aperture having an inner wall surface, and the reflecting circumferential surface is formed by the inner wall surface of the aperture. This embodiment of the invention is preferred in terms of material requirement and weight of the intermediate body. The reflecting circumferential surface is formed by the inner wall (inner curved surface) of the aperture. As a preference in terms of production technology, and in accordance with another feature of the invention, the intermediate body is a hollow cylinder.
In accordance with a further feature of the invention, the circumferential surface is shaped as a barrel or a drum. The term xe2x80x9ccircumferential surfacexe2x80x9d herein means the inner wall of the aperture or the outer curved surface of the solid intermediate body. The barrel or drum design enables a particularly high proportion of the reflected radiation portion to be directed onto the reception zone.
In accordance with again an added feature of the invention, the intermediate body is a molded plastic body. Production costs are very low in plastics processing and production technology in plastic molding technology allows very accurate yet inexpensive devices.
In accordance with again a further feature of the invention, the intermediate body is a solid, molded plastic body and the reflecting circumferential surface is formed by a curved surface of the plastic body.
In accordance with a concomitant feature of the invention, a lens is integrally formed on the intermediate body, and the lens forms the reflection surface. This embodiment further simplifies the design and reduces the number of individual parts to be handled and positioned during assembly.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in an optical transmission device, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.